Extraordinary Design


Coalescing oil water separators

The Mercer Advantage

For over 50 years there has been tension in the design of mainstream oil/water coalescers.  Traditionally, those coalescers that were tightly packed to get the best efficiency numbers fouled very quickly.  Conversely, those designed to require less maintenance and cleaning were unable to meet mandatory removal levels.  What Mercer International has done is design a solution that combines the highest possible efficiency with the lowest practical maintenance.

At the heart of this solution is Mercer’s Multi-Pack™ removable plate coalescer, a patented system utilizing flat parallel-plate coalescer modules with removable and adjustable plates. The most important evolution in the oil water separation arena came when Mercer created dedicated zero turbulence chambers ("Chimney Zones") for solids removal and oil extraction. The ability to remove solids from the process flow, as well as the other design improvements below, have led to  Mercer International's reputation for being the highest performance oil water separator on the market.

flat plate coalescer

Flat Plate Herring-Bone Design (55 degree angle)

The Multi-Pack™ utilizes time-honored flat parallel plates set at a steep 55 degree angle. The smooth flat plates and cross-flow design help make this the most non-plugging design that industry has to offer. Utilizing this "Short Plate Width" design concept, coalescer plate gaps can be tighter with less plugging than traditional coalescer plate designs.

low maintenance oil water separator

Chimney Zones™

The Multi-Pack design offers an independent collection chamber for both oil and solids. As solids fall off the top of the impingement plates (or as oil droplets coalesce and rise up and out of the coalescer plates) they enter a “zero velocity” baffled Chimney Zone. Keeping solids and oils separator reduces sludge and pre-mature fouling.

coalescer flow distribution

Oil Water Separator Inlet/Outlet Flow Distribution Baffles

Mercer is one of the very few separator manufacturers that continues to provide efficient, two-stage distribution baffles. Our two-stage distribution baffle system is designed to assure evenly dispersed flow over the entire entry area of the coalescer — offering superior results within the coalescer.

versatile oil water separators

Field Adjustable Removable Plates

Each plate within the coalescer is completely removable from the coalescer frame and the plate spacing is therefore able to be adjusted to multiple plate gap settings on site. This patented feature lets the operator easily field adjust the coalescer to obtain optimal results.

hopper style sludge coalescer

Hopper Bottom Design

Angles of incidence are a steep 55° angle from the horizontal axis. In an aqueous environment, this is an excellent angle for most solids to overcome friction-forces-per-relative-weight in a liquid carrier, and effectively move solids down to the bottom, without binding on the hopper walls. By simple geometry, for a given tank width, the steeper the angle of incidence the higher solids-holding capacity.

industrial oil water separators

Sturdy Tank Design and Paint System

Mercer supplies a sturdy tank shell to house the internal components. Our separators built in the mid-range size (400-600 gpm) have exterior shell walls from 5/16” to 3/8”, with 3/4” base plates and substantial structural reinforcing. We utilize schedule 80 carbon steel or stainless steel sludge fittings where blasting and painting is the most difficult and the effects of corrosion will be the most prominent.

cleaning oil water separators

Ease of Cleaning

A coalescer that processes oils and solids out of the pack will inherently extend the time between cleaning significantly. Furthermore, Mercer's flat-plate herring-bone design is the industry's easiest coalescer to clean.

weir plates

Full Width Weir Plate Design

The weir plate is designed to run the full width of the separator. This helps suppress unwanted surges within the unit. This is important when skim pipes. If the skim pipes can not be set properly because of excessive surging, either no oil will enter the oil holding tank, or too much water will enter the compartment. Weir plate add system versatility.

oil water separator accessories


Mercer has a number of standard and custom accessories available. Typical accessories include: automatic oil skimmer, level alarm/control systems, electric heaters to prevent freezing, insulation, oil-stop valves, early warning oil spill systems, automated solids removal valves, sludge capture systems, and more.


Materials of Construction

As the specifications have moved to 30 year shelf lives in oil water separator design, it's increasingly important to explore the metal options that stand up better to the test of time.